Implanted pacemakers and intracardiac cardioverter defibrillators (ICD) deliver therapy to patients suffering from various heart-diseases (Clinical Cardiac Pacing and Defibrillation—2nd edition, Ellenbogen, Kay, Wilkoff, 2000). It is known that the cardiac output depends strongly on the left heart contraction in synchrony with the right heart (see U.S. Pat. No. 6,223,079). Congestive heart failures (CHF) is defined generally as the inability of the heart to deliver enough blood to meet the metabolic demand. Often CHF is caused by electrical conduction defects. The overall result is a reduced blood stroke volume from the left side of the heart. For CHF patients a permanent pacemaker with electrodes in 3 chambers, that are used to re-synchronize the left heart contraction to the right heart is an effective therapy, (“Device Therapy for Congestive Heart Failure”, K. Ellenbogen et al, Elsevier Inc. (USA), 2004). The resynchronization task demands exact pacing management of the heart chambers such that the overall stroke volume is maximized for a given heart rate (HR), where it is known that the key point is to bring the left ventricle to contract in synchrony with the right ventricle. Clearly, the re-synchronization task is patient dependent, and with each patient the best combination of pacing time intervals that restores synchrony are changed during the normal daily activities of the patient. For these reasons, next generation cardiac re-synchronization therapy devices should have online adaptive capabilities according to Hemodynamic performance. In a recent publication by D. Odonnell et al titled, “Long-Term Variations in Optimal Programming of Cardiac Resynchronization Devices”, PACE 28; January 2005; 24-26, the authors reported the results of a clinical study with 40 CHF patients. The authors found that the optimal atriaventricular (AV) delay and VV interval, obtained using echocardiography, varied significantly during 9 months of patient follow-ups. The authors explained the results by a slow and gradient improvement in the cardiac function due to the implanted CRT devices that generated a reverse remodeling of the left ventricle.
Currently available cardiac resynchronization therapy (CRT) devices have drawbacks that prevent the achievement of an optimally delivered CRT and are listed:—
1. Programming and troubleshooting CRT device—Optimizing the CRT device using echocardiography is expansive, time consuming and operator dependent. The clinician should optimize both the AV delay, in order to achieve maximal diastolic filling time, and the interventricular delay (W interval) in order to achieve resynchronisation of heart chambers contractions.2. Consistent Delivery of CRT—There are several reasons why CRT is not delivered consistently, and some times is not delivered at all for hours. Examples are failure to optimise the AV delay and low maximal tracking rate.3. Follow Ups—The clinician must perform the complex task of optimization and programming of the CRT device, first at implantation and then at each follow-up.4. CRT non-responders, 30% of the patients do not respond to CRT.
AV delay optimization in dual chamber pacemakers and defibrillators are as important clinically as the AV delay optimization of CRT devices. Dual chamber devices use one atrial electrode and one ventricular electrode, and a ventricular pacing occurs after the pre-programmed AV delay measured from a sensed or paced atrial event ends. The AV delay depends on the heart rate and on the stress conditions which vary from patient to patient. Furthermore, the AV delay of a patient varies depending on the daily activities. Therefore a fixed pre-programmed AV delay scheme is less then optimal. Loss of AV synchrony is a major cause for a pacemaker syndrome as quoted in Beyerbach D. M. and Cadman C. Oct. 10, 2002, in http://www.emedicine.com/med/topic2919.htm “Pacemaker Syndrome”, the contents of which are incorporated herein by reference. Ellenbogen et al. cited above, focused on clinical utility and proposed that “pacemaker syndrome represents the clinical consequences of AV dyssynchrony or sub-optimal AV synchrony, regardless of the pacing mode.”
Artificial neural networks are known for their superior performance in processing in performing tasks as compared to standard algorithmic processing, such as adaptive control and pattern recognition. The spiking neural networks architecture is a unique form of artificial neural networks that are inspired by the biological nerve system. Spiking neurons architectures, applications and learning rules are reviewed by Wolfgang Maass et. al. “Pulsed Neural Network”, The MIT Press, London England (2001). Rate responsive heart stimulation device using neural networks has been proposed in U.S. Pat. No. 5,782,885